1. Field of the Invention
The present invention relates to a thermal activator for a heat sensitive adhesive sheet comprised of a sheet-like base material formed with a heat sensitive adhesive layer normally exhibiting a non-adhesive property and exhibiting an adhesive property when heated on one side thereof, and to a printer apparatus utilizing the thermal activator and, more particularly, to a technique that makes it possible to prevent a heat sensitive adhesive or a denatured product of the heat sensitive adhesive from adhering to transport means or to remove the same.
2. Description of the Related Art
Recently, heat sensitive adhesive sheets (heat sensitive adhesive labels) as one type of so-called linerless labels are used in various fields, e.g., for applying POS labels for foods, labels for physical distribution and delivery, labels for medical use, baggage tags, and indication labels for bottles and cans.
Such a heat sensitive adhesive label is configured by forming a heat sensitive adhesive layer normally exhibiting a non-adhesive property and exhibiting an adhesive property when heated and a printable surface on the bottom and top of a sheet-like label base material (e.g., base paper), respectively. The heat sensitive adhesive is mainly composed of a thermoplastic resin, a solid-state plasticizer, and the like and is characterized in that is exhibits a non-adhesive property at the room temperature but exhibits an adhesive property when heated and activated by a thermal activator. Normally, the activation temperature is in the range from 50 to 150° C., and the solid-state plasticizer in the heat sensitive adhesive is melted in that temperature range to impart the adhesive property to the thermoplastic resin. Since the solid-state plasticizer thus melted is gradually crystallized after being put in an over-cooled state, the adhesive property is maintained for a predetermined time, and the adhesive is used for applying something to an object such as a glass bottle while it has the adhesive property.
For example, a printable surface of a heat sensitive adhesive label is constituted of a heat sensitive coloring layer; and desired characters, images, and the like are printed thereon by a common thermal printer apparatus having a thermal head; and the heat sensitive adhesive layer is activated by the thermal activator.
Printer apparatus are under development in which the thermal activator is loaded in the thermal printer apparatus to allow heat sensitive printing on a heat sensitive label and activation of the heat sensitive adhesive layer to be performed continuously.
For example, such printer apparatus have had a configuration as shown in FIG. 17.
In FIG. 17, reference sign P2 represents a thermal printer unit; reference sign C2 represents a cutter unit; reference sign A2 represents a thermal activation unit; and reference sign R represents heat sensitive adhesive labels that are wound in the form of a roll.
The thermal printer unit P2 has a thermal head 100 for printing, a platen roller 101 that is urged into contact with said thermal head 100 for printing, and a driving system that is not shown (e.g., an electric motor, a gear train, and the like) for rotating the platen roller 101.
The platen roller 101 is rotated in a direction D1 (clockwise) in FIG. 17 to pull out a heat sensitive adhesive label R and to transport it in a direction D2 (to the right) after heat-sensitive printing is performed on the heat sensitive adhesive label R thus pulled out. The platen roller 101 also has pressing means that is not shown (e.g., a coil spring, a plate spring, or the like), and a surface of the platen roller 101 is urged by a repellent force of the same into contact with the thermal head 100. For example, the heat sensitive label R has a configuration as shown in FIG. 17.
Specifically, a thermal coat layer 501 as a heat sensitive coloring layer for forming a printable surface is provided on one side of base paper 500 as a label base material (on the top of the same in FIG. 18), and a color printing layer 502 having characters, patterns and the like of a frame of a price tag, a unit, and the like printed thereon is formed on the same. On the other side of the base paper 500 (the bottom of the same in FIG. 18), there is formed a heat sensitive adhesive layer K on which a heat sensitive adhesive mainly composed of a thermoplastic resin, a solid-state plasticizer, and the like is applied.
The thermal head 100 for printing and the platen roller 101 operate based on a printing signal from a printing controller that is, not shown, whereby printing can be performed as desired on the thermal coat layer 501 of the heat sensitive adhesive label R.
The cutter unit C2 is for cutting the heat sensitive adhesive label R that has been subjected to the heat sensitive printing by the thermal printer unit P2 into an appropriate length, and it is constituted of a movable blade 200 operated by a driving source (that is omitted in the illustration) such as an electric motor, a fixed blade 201, and the like. The movable blade 200 is operated at predetermined timing under control of a controller that is not shown.
For example, the thermal activation unit A2 is rotated by a driving source that is not shown, and it has a roller 300 for insertion and a roller 301 for ejection for inserting and ejecting the cut heat sensitive adhesive label R. A thermal head 400 for thermal activation and a platen roller 401 that is urged into contact with the thermal head 400 for thermal activation are disposed between the roller 300 for insertion and the roller 301 for ejection. The platen roller 401 has a driving system that is not shown (e.g., an electric motor, a gear train, and the like) and rotates the platen roller 401 in a direction D4 (counterclockwise in FIG. 17) to transport the heat sensitive adhesive label R in a direction D6 (to the right in FIG. 17) with the roller 300 for insertion and the roller 301 for ejection that rotate in a direction D3 and a direction D5. The platen roller 401 has pressing means that is not shown (e.g., a coil spring, a plate spring, or the like), and a surface of the platen roller 401 is urged into contact with the thermal head 400 for thermal activation by a repellent force of the same.
Reference sign S represents an ejection detecting sensor for detecting the ejection of the heat sensitive adhesive label R. The next heat sensitive adhesive label R is printed, transported, and thermally activated based on the detection of the ejection of the heat sensitive adhesive label R by the ejection detecting sensor S. The thermal head 400 for thermal activation and the platen roller 401 are operated at predetermined timing by a controller that is not shown, and the heat sensitive adhesive layer K of the heat sensitive adhesive label R is activated by heat applied by the thermal head 400 for thermal activation to exhibit adhesion.
After the heat sensitive adhesive label R is made adhesive by the thermal activation unit A2 having such a configuration, an operation of applying an indication label to a glass bottle such as a liquor or medicine bottle, a plastic container or the like or an operation of applying a price tag or advertising label is carried but. This is advantageous in that a cost reduction can be achieved because there is no need for a release sheet (liner) unlike a conventional and common adhesive label sheet and also advantageous in view of resource saving and environmental problems because there is no need for a release sheet that becomes a waste after use.
However, the thermal activation unit A2 for the conventional heat sensitive adhesive label R has had a problem in that the heat sensitive adhesive and a product of denaturation of the heat sensitive adhesive (a substance as a result of a chemical change or carbonization of the same due to heat) can adhere to the transport means for the heat sensitive adhesive label R (the platen roller 401, in particular).
Specifically, when a heat sensitive adhesive label R leaves the platen roller 401 after the heat sensitive adhesive layer K of the heat sensitive adhesive label R cut into a predetermined length by the cutter unit C2 is heated and activated by a heating element H of the thermal head 400 for thermal activation, as shown in FIG. 19(a), a part of the heat sensitive adhesive of the heat sensitive adhesive layer K is squeezed into the gap between the platen roller 401 and the thermal head 400 for thermal activation as a result of softening of the same attributable to heating, the part being thus released from the base paper 500 of the heat sensitive adhesive label R.
The platen roller 401 temporarily enters an idle running state as the heat sensitive adhesive label R is ejected, and heat sensitive adhesive G1 in a separated state as shown in FIG. 19(a) adheres to a circumferential surface of the platen roller 401 because of adhesion resulting from activation, as shown in FIG. 19(b).
After the states shown in FIGS. 19(a) and 19(b) are repeated a plurality of times, a multiplicity of lumps of the heat sensitive adhesive G1 adhere to the circumferential surface of the platen roller 401, as shown in FIG. 19(c). The heat sensitive adhesive G1 thus deposited is repeatedly heated by the thermal head 400 for thermal activation to be chemically changed or carbonized into a denatured product G2 that can rigidly adhere to the circumferential surface of the platen roller 401.
Further, since the heat sensitive adhesive G1 that has adhered to the circumferential surface of the platen roller 401 has a high adhesive force because it has been melted by being heated by the thermal head 400 for thermal activation a plurality of times, a part of the same can adhere to the top side of a heat sensitive adhesive label R that is transported to the same to smear and damage the printing surface thereof.
The smoothness of the circumferential surface of the platen roller 401 is reduced by the multiplicity of lumps of the heat sensitive adhesive G1 that adhere to the same, which has resulted in a problem in that the heat sensitive adhesive layer K of a heat sensitive adhesive label R transported thereto can not be uniformly heated and is therefore unable to exhibit sufficient adhesion.